#include<stdio.h>
#include<math.h>
int main()
{
	float x1,x2,y1,y2,distance;
	while(scanf("%f %f %f %f",&x1,&y1,&x2,&y2)!=EOF)
	{
		distance=sqrt(((x2-x1)*(x2-x1))+((y2-y1)*(y2-y1))); 
		printf("%.2f",distance);
	}
	return 0;
 } 
